The present invention relates to a rotation angle detecting apparatus for detecting a rotation angle and a surveying instrument which uses the rotation angle detecting apparatus.
As an apparatus for detecting a rotation angle, there is a rotation angle detecting apparatus, and the rotation angle detecting apparatus is used as an angle detector in case of detecting an elevation angle or a horizontal angle in a surveying apparatus.
The miniaturization and the high accuracy of recent surveying instrument are demanded, and further, a reduction in cost is also demanded.
For example, as a surveying instrument using a rotation angle detecting apparatus, there is a total station, and the total station measures a distance to a object to be measured, and an elevation angle or a horizontal angle of the object to be measured.
In the measurement errors of the total station, an error of a measurement value due to an angular error corresponds to a product obtained by multiplying the angular error by the distance to a object to be measured, and the error of the measurement value is proportionate to the distance. Therefore, an angular accuracy is demanded to a degree of a second. As one of causes of an increase in price of the total station, there is a demand for a high accuracy of an angle detection accuracy and a rotation accuracy.
As the rotation angle detecting apparatus for use in the surveying instrument, a highly accurate encoder has been conventionally used, however, an accuracy of each component constituting the encoder or the stability after assembling is a problem, and the highly accurate encoder is expensive. Further, since an angular error is caused due to a fabrication error of the encoder itself and a detection error as well as a rotational error owing to the runout of a rotation shaft. Therefore, it is difficult to set an angle detection accuracy to a demanded accuracy, just by managing a processing accuracy of a lone component, and the fine adjustment and fine finishing in an assembling state of a rotation shaft and a bearing holder are required, which results in expensiveness.